Convert UI interface to boost::signals2.

- Signals now go directly from the core to WalletModel/ClientModel.
  - WalletModel subscribes to signals on CWallet: Prepares for multi-wallet support, by no longer assuming an implicit global wallet.
- Gets rid of noui.cpp, the few lines that were left are merged into init.cpp
- Rename wxXXX message flags to MF_XXX, to make them UI indifferent.
- ThreadSafeMessageBox no longer returns the value `4` which was never used, converted to void.

src/qt/qtipcserver.cpp

@@ -31,7 +31,7 @@ void ipcThread(void* parg)
         ptime d = boost::posix_time::microsec_clock::universal_time() + millisec(100);
         if(mq->timed_receive(&strBuf, sizeof(strBuf), nSize, nPriority, d))
         {
-            ThreadSafeHandleURI(std::string(strBuf, nSize));
+            uiInterface.ThreadSafeHandleURI(std::string(strBuf, nSize));
             Sleep(1000);
         }
         if (fShutdown)
@@ -69,7 +69,7 @@ void ipcInit()
             ptime d = boost::posix_time::microsec_clock::universal_time() + millisec(1);
             if(mq->timed_receive(&strBuf, sizeof(strBuf), nSize, nPriority, d))
             {
-                ThreadSafeHandleURI(std::string(strBuf, nSize));
+                uiInterface.ThreadSafeHandleURI(std::string(strBuf, nSize));
             }
             else
                 break;